Physiological and growth indexes determination
Chlorophyll content in the P. massoniana seedling leaves was determined referring previous report.18 Leaf net photosynthetic rate (Pn) was measured with a portable photosynthesis system (Li-6400, Li-Cor, Lincoln, NE, USA) following our previous instrument operation.18At least 10 samples were randomly selected from the seedlings under each Ca level.
For the measurement of Ca content in the leaves, the leaf tissue were initially dried at 80°C, then ashed at 550°C and dissolved in concentrated HNO3 and digested using a microwave digestion machine (MARS6, CEM, USA). Finally, an ICP-MS based element analysis was performed.22
To access the biomass of the seedlings grown at different Ca levels, the dry weight of seedling were measured. Seedlings were oven-dried (80°C) to constant weight and measured with an analytical balance.
Soluble protein content were measured referring Qiao et al.23 Oxidation stress related parameters, leaves hydrogen peroxide (H2O2) content, total ascorbate peroxidase (APX) activity and total superoxide dismutase (SOD) activity were detected follow previous procedures.24